Method for improving the fatigue life of a tubular stabilizer bar

Abstract

An autofrettage process employed on the inner surface of a tubular stabilizer bar. Road shock and other vibrations subject the stabilizer bar to tensile stresses. Tensile stresses cause fractures and decrease the fatigue life of the bar. In employing an autofrettage process, a pressurized fluid is introduced into the interior space of a sealed stabilizer bar, slightly increasing the inner diameter of the stabilizer bar. As the inner surface of the stabilizer bar is deformed, residual compressive stress forces are created which counteract and oppose the tensile stress forces. The residual compressive stress forces prevent the tensile stresses from fracturing the inner surface of the bar, increasing fatigue life. A shot peening process can be employed on the exterior surface of the bar to create residual compressive stress forces which counteract exterior tensile forces.

What is claimed is:  
     
       1. A method for improving the fatigue life of a tubular stabilizer bar of a vehicle suspension system having a plurality of bends and an inner diameter comprising the steps of: 
       sealing an end of said stabilizer bar;  
       pressurizing an internal surface of an entire length of said stabilizer bar to plastically deform said internal surface to a deformed inner diameter; and  
       producing a plurality of compressive forces on said internal surface.  
     
     
       2. The method as recited in  claim 1  wherein said internal surface is pressurized by a hydraulic fluid. 
     
     
       3. The method as recited in  claim 2  wherein said hydraulic fluid is oil. 
     
     
       4. The method as recited in  claim 2  wherein the step of pressurizing said internal surface of said stabilizer bar includes injecting said hydraulic fluid in an opposing end of said stabilizer bar. 
     
     
       5. The method as recited in  claim 1  wherein the step of pressurizing said internal surface of said stabilizer bar further includes pressurizing said plurality of bends on said interior surface of said stabilizer bar. 
     
     
       6. The method as recited in  claim 1  wherein said deformed inner diameter is greater than said inner diameter. 
     
     
       7. The method as recited in  claim 1  wherein the step of pressurizing said internal surface of said stabilizer bar further includes applying a predetermined pressure. 
     
     
       8. The method as recited in  claim 1  wherein the step of pressurizing said internal surface of said stabilizer bar is applied for a predetermined amount of time. 
     
     
       9. The method as recited in  claim 1  wherein said plurality of compressive forces counteract a plurality of tensile forces. 
     
     
       10. The method as recited in  claim 1  wherein the step of sealing an end of said stabilizer bar includes employing a clamp. 
     
     
       11. The method as recited in  claim 1  wherein the step of pressurizing said internal surface of said stabilizer bar further includes not substantially changing an outer diameter of said stabilizer bar. 
     
     
       12. The method as recited in  claim 1  wherein the steps of sealing an end of said stabilizer bar, pressurizing said internal surface, and producing said plurality of compressive forces occur after a step of forming said stabilizer bar. 
     
     
       13. A method for improving the fatigue life of a tubular stabilizer bar of a vehicle suspension system having a plurality of bends and an inner diameter comprising the steps of: 
       sealing an end of said stabilizer bar;  
       pressurizing an internal surface of an entire length of said stabilizer bar to plastically deform said internal surface to a deformed inner diameter and to produce a plurality of compressive forces on said internal surface; and  
       pressuring an exterior surface of said stabilizer bar by a shot peening process utilizing a plurality of beads.  
     
     
       14. The method as recited in  claim 13  wherein said internal surface is pressurized by a hydraulic fluid. 
     
     
       15. The method as recited in  claim 14  wherein said hydraulic fluid is oil. 
     
     
       16. The method as recited in  claim 13  wherein the step of pressurizing said internal surface of said stabilizer bar further includes pressurizing said plurality of bends on said interior surface of said stabilizer bar. 
     
     
       17. The method as recited in  claim 13  wherein said deformed inner diameter is greater than said inner diameter. 
     
     
       18. The method as recited in  claim 13  wherein the step of pressurizing said internal surface of said stabilizer bar further includes applying a predetermined pressure. 
     
     
       19. The method as recited in  claim 13  wherein the step of pressurizing said internal surface of said stabilizer bar is applied for a predetermined amount of time. 
     
     
       20. The method as recited in  claim 13  wherein said plurality of compressive forces counteract a plurality of tensile forces. 
     
     
       21. The method as recited in  claim 13  wherein the step of sealing an end of said stabilizer bar includes employing a clamp. 
     
     
       22. A method for improving the fatigue life of a tubular stabilizer bar of a vehicle suspension system having a plurality of bends and an inner diameter comprising the steps of: 
       sealing an end of said stabilizer bar;  
       pressurizing an internal surface of an entire length of said stabilizer bar to plastically deform said internal surface to a deformed inner diameter and not substantially changing an outer diameter of said stabilizer bar; and  
       producing a plurality of compressive forces on said internal surface.